This invention relates to bending of glass sheets and in particular to a glass sheet shaping system which utilizes a double-faced vacuum mold arrangement to shape and move heat softened glass sheets from a shaping station to two independent transferring and cooling stations.
Shaped glass sheets are widely used as windshields, side windows or rear windows in vehicles such as automobiles and the like. To be suitable for such applications, flat glass sheets must be shaped to precisely defined curvatures dictated by the shape and outline of the frames defining the window openings into which the glass windows are installed. It is also important that the windows meet stringent optical requirements and that they be free of optical defects that would tend to interfere with the clear viewing through their viewing area.
During fabrication, the glass sheets may be subjected to thermal treatment to control internal stresses. In particular, glass sheets used for windshields are normally annealed to reduce the internal stresses while glass sheets used for side windows or rear windows are tempered to induce compressive stresses in the major surfaces of the sheets and tensile stresses in the center regions. Tempering strengthens the glass and increases its resistance to damage resulting from impact.
In the heating and shaping of glass sheets for windshields, it is common practice to use contoured bending rings that support one or more flat glass sheets and convey it through a heating lehr. As the temperature of the glass increases and approaches its heat softening temperature, it begins to sag under the force of gravity and conforms to the contours of the shaping rails on the mold. If desired, additional presses may be used to shape the glass sheets while supported on the ring.
During the commercial production of tempered glass sheets for sidelights and backlights, a glass sheet is generally conveyed along a substantially horizontal path through a tunnel-type furnace, heated to its heat softening temperature and transferred into a shaping station adjacent the furnace where the glass sheet is shaped. After shaping, the shaped glass sheet is transferred to a cooling station where it is controllably cooled. The heat softened glass sheet may be shaped, for example, by pressing the sheet between a pair of upper and lower shaping surfaces such as that disclosed in U.S. Pat. No. 4,272,274 to Frank et al., U.S. Pat. No. 4,662,925 to Thimons et al. and U.S. Pat. No. 4,830,650 to Kelly. The glass sheets may also be formed by a shaping arrangement which incorporates two distinct shaping surfaces. For example, U.S. Pat. No. 5,286,271 to Rueter et al., glass sheets enter a shaping station and are pressed against one of the shaping surfaces of a mold having two shaping surfaces. The mold then transfers the shaped sheet to a series of curved conveying rolls which advance the glass sheet into a cooling station while supporting the glass to maintain its contoured configuration. U.S. Pat. No. 5,320,661 to Fecik et al. discloses an arrangement whereby flat glass sheets are lifted by a flat vacuum pickup and transferred to one of two shaping stations positioned adjacent to sheet pickup area where the sheet is pressed to shape. The sheet is then transferred onto a tempering ring and moved to a cooling station positioned near the corresponding shaping station.
It would be beneficial to have a glass sheet shaping arrangement that provides for high speed shaping of glass sheets while maintaining high optical quality and shape control and in addition allows for the shaping of successive glass sheets to different configurations.